1. Field of the Invention
The present invention generally relates to a glass plate and a method for manufacturing the glass plate.
2. Description of the Related Art
In recent years, glass plates have been manufactured for the use of image display apparatuses such as liquid crystal displays and organic EL (Electro Luminescence) displays. For example, a glass substrate may be used as a glass plate on which a function layer such as a thin film transistor (TFT) or a color filter (CF) is formed. Further, a glass plate may be used as a cover glass for improving the aesthetics of a display or increasing protection of the display.
As a method for strengthening a glass plate, a chemical strengthening method is developed. With the chemical strengthening method, a chemically strengthened layer (compression stress layer) having a predetermined depth from a front surface of a glass plate is formed on the glass plate by using a process liquid used for ion-exchange. A tensile stress layer is formed inside the chemically strengthened glass plate for maintaining balance of stress.
In a case where a glass plate is bent, compression stress is generated in a main flat surface corresponding to a concave surface of the glass plate whereas a tensile stress is generated in a main flat surface corresponding to a convex surface of the glass plate. In this case, when a minute scratch exists at a border part between the main flat surface corresponding to the convex surface of the glass plate and an end surface adjacent to the main flat surface corresponding to the convex surface of the glass plate, the scratch may become the cause for breakage of the glass plate.
Therefore, there is proposed a glass plate including a chamfered surface formed at the border part in which a valley part of the chamfered surface has a maximum valley depth Rv less than or equal to 2 μm (see, for example, International Publication Pamphlet 10/104,039). In a case where the maximum valley depth Rv is less than or equal to 2 μm, the valley part can be prevented from being torn by controlling the stress concentrating on the trough part. Thereby, breakage of the glass plate can be prevented. International Publication Pamphlet 10/104,039 also proposes a glass plate in which the valley part of a chamfered surface has a projecting valley depth Rvk less than or equal to 0.95 μm.
When an end surface of a glass plate is grinded by a rotating grinding wheel, a micro-scratch may be formed on the end surface. The micro-scratch is a minute scratch that is difficult to visually recognize. The micro-scratch may cause degradation of flexural strength of a glass plate. Because micro-scratches are likely to be formed inside the glass plate, accurate evaluation of, for example, flexural strength cannot be performed based on the above-described depth Rv or depth Rvk.